1. Field of the Invention
The present invention is directed to a low cost high efficiency steam heating system, and more particularly to a steam heating system especially adapted to maintain a generally constant temperature in a relatively small space, i.e. in a single zone system using one or more radiators such as may be found in a single dwelling home or apartment.
2. The Prior Art
Conventional steam heating systems of the single dwelling-single zone type are notoriously inefficient in that the temperature in the space is rarely maintained at or near a desired set point. Typical systems of the type described employ a thermostat in the space to be heated which controls a fuel burner, which in turn heats a boiler. Upon a call for heat at the thermostat, steam is generated in the boiler and as the steam pressure increases the steam enters the piping system forcing cool air through the thermostatic vent valves. These valves allow the cool air within the radiators and piping system to vent to the atmosphere and close when steam enters the radiators.
After venting of the air, the hot steam heats the cast iron radiators, which continue to emit heat energy to the space. The burner continues to function until the temperature setting of the thermostat is reached. At this point the burner is deactivated.
A significant drawback of such conventional systems resides in the fact that the radiation equipment will continue to emit heat after the set point is reached and after the burner is deactivated, such residual heat raising the temperature within the space beyond the desired set point. As a result, there is a continuous "hunting" cycle wherein the temperature in the space continuously varies from a temperature below the set point to a temperature above the set point, the higher temperature being developed, as noted, as a result of the continued emission of heat after the set point has been reached.
Numerous control systems have been proposed which incorporate complex valving, multiple sensors etc. in an attempt to provide a relatively constant temperature within one or more spaces to be heated. Such assemblies have heretofore been expensive in view of their complexity, trouble prone, and generally unsuited to simple single zone applications.
Representative examples of prior art control systems include the following:
Patent 1,992,846 relates to a system in which the temperature of the radiator rather than the surrounding space controls the steam supply. Accordingly, the time of steam flow is a function of air temperature surrounding a pilot radiator, rather than purely a function of the condition of the temperature adjacent the thermostat.
Patent 2,468,268 discloses an intermittently fired steam producer in combination with means for heating radiators between cycles, the heating being dependent upon the differential of indoor and outdoor temperatures. When pressure drops due to a high temperature differential, the pressure drop induces a heat flow through the heating circuit even during the off cycle of the boiler.
Other examples of steam heating systems may be found the following additional U.S. Patents:
______________________________________ 1,985,215 (Shivers) 2,030,544 (Ross) 2,062,565 (Ferguson et al) 2,065,198 (Rohlin) 2,152,699 (Kuester et al) 2,153,382 (Martin Jr.) 2,249,706 (Furguson) 2,378,760 (Furguson) 2,387,576 (Graves) 2,668,664 (Williams) ______________________________________
It is also known, for instance in multi-zone hot water heating systems to provide a boiler which incorporates a temperature control which continually keeps the water at a predetermined temperature irrespective of whether any zone or zones call for heat. In such systems a series of valves and pumps are energized even during off cycles of the boiler to satisfy the needs of respective zones.
Such systems are wasteful of energy since water in the system will be heated even though the temperature in the various zones never goes below the set point of the control thermostats.